Mercury-wetted contact switch



Sept. 30, 1969 KODA ET AL 3,470,502

' MERCURY-WETTED CONTACT SWITCH Filed 001. 11, 1967 x I N :11 Ir; ggmuu; 5 144: 1' I I v 4 5' 54 3i Z: 344 u 20g 3 I I Q.

United States Patent "ice 3,470,502 MERCURY-WETTED CONTACT SWITCH Arthur J. Koda, Morton Grove, and John Kutyla, Chicago, Ill., assignors to (I. P. Clare & Company, Chicago, Ill., a corporation of Delaware Filed Get. 11, 1967, Ser. No. 674,459 Int. Cl. Hillh 29/00 U.S. Cl. 335-47 Claims ABSTRACT OF THE DISCLOSURE A high speed mercury-wetted contact switch having a sealed glass housing in the upper end of which two magnetic terminals are sealed. A header sealed in the lower end of the housing carries a pivotal or hinge support for one end of a short, rigid, and mercury-wetted armature whose upper end is disposed between the contacts. The header and pivot structure provide a restricted flow path for mercury from a mercury pool in the lower end of the housing to limit mercury accumulated on the armature and permit hi h speed operation. The pivot structure, which is lubricated with mercury, provides bias free movement of the armature limited only by engagement with the terminal at speeds up to 800 cycles per second with little jitter.

This invention relates to a glass enclosed contact unit and, more particularly, to a new and improved mercurywetted contact device.

Mercury-Wetted contact units or switches, such as those shown and described in US. Patents Nos. 2,868,926 and 3,054,873, are well suited for high volume switching ap plications because of their uniform low contact resistance and long operating life in even extremely adverse environments. However, efforts to use these contact units in repetitive drive applications, such as choppers in which operating speeds in excess of one hundred cycles per second are desired, have not been particularly successful. Although these contact units are capable of operating at speeds in excess of two hundred cycles per second, they present excessive jitter, i.e., instability of operate and release characteristics with constant drive applications, beyond one hundred cycles per second. This appears to be due to the large and varying mass of the moving flexible armature as drive conditions and resonance affect the quantity and distribution of mercury on its surface. Attempts to obviate excessive jitter at higher speeds or rates of operation by reducing the mass of the armature, e.g., by shortening or narrowing it, have not been successful because of the effects on the sensitivity of the switch unless corresponding reductions in the flexibility or thickness of the armature are made. Further, these changes in the flexible armature frequently cause premature magnetic saturation of the armature as well as substantially poorer vibration and shock characteristics.

Accordingly, one object of the present invention is to provide a new and improved mercury-wetted contact unit or switch,

Another object is to provide a mercury-wetted contact switch operable without appreciable jitter at speeds greatly in excess of switches now known.

A further object is to provide a mercury-wetted contact switch having a freely pivotable mercury-wetted armature.

Another object is to provide such a switch including new and improved means for controlling the splashing of mercury.

A further object is to provide a sealed mercury switch unit including a rigid rnercury-wetted magnetic armature 3,470,502 Patented Sept. 30, 1969 movable into engagement with a contact at one end and mounted for free pivotal movement at the other end limited only by engagement with the contact.

A further object is to provide a sealed mercury switch including a short rigid armature freely pivoted or hinged at one end on a mercury-wetted hinge or pivot structure.

A further object is to provide a sealed mercury-Wetted contact switch including a rigid armature that is freely pivotable about a hinge structure at one end and which has a length in the range from .100 to .200 inch.

A further object is to provide a sealed mercury-wetted contact switch unit including a short rigid armature that is freely pivotable into alternate engagement with spaced contacts completely free of mechanical stress or bias.

Another object is to provide a mercury-wetted contact unit including a short rigid armature pivotally mounted at one end for movement into alternate engagement with spaced contacts, which armature is pivoted at one end by a hinge or pivot structure spaced substantially above a pool of mercury for wetting the armature surface.

In accordance with these and many other objects, an embodiment of the invention comprises a sealed mercurywetted contact switch capable of substantially jitter-free operations at speeds greatly in excess of those switches known or used in the past. The sealed mercury switch comprises an elongated glass housing in one end of which are sealed a pair of spaced magnetic terminals including contact portions disposed within the sealed cavity of the housing, which contact portions also serve as motion limiting members. A hollow header is sealed in the opposite end of the elongated housing and includes a flat portion on its inner end to which is secured one part of a hinge or pivotal mounting structure for a short, rigid, and mercury-wetted armature. The other part of the hinge or pivot structure is secured to the lower end of the armature, and the upper end of the armature is interposed between the spaced contacts. The pivot structure, which is mercury-wetted so as to provide mercury lubrication for the pivotal movement, permits completely free pivotal or hinged movement of the rigid armature limited only by engagement of the armature with the contacts, free of any restraining bias or mechanical stress. This arrangement coupled with the short and rigid nature of the armature permits operation of the switch at repetition rates as high as eight hundred cycles per second with a jitter of less than fifty microseconds, as contrasted with longer periods of jitter with prior switches at repetition rates around fifty to sixty cycles per second.

To permit the operation of the switch at these high speeds without accumulating excessive mercury at the top of the armature or the top of the switch, the hinged or pivotal supporting structure for the short, rigid armature is displaced substantially above the reservoir or pool of mercury to restrict the flow of mercury to the capillary surfaces on the armature. In addition, the armature is terminated immediately above the contact portions, and a transverse plate is secured to the top of the armature having a transverse dimension at least equal to the gap between the spaced contacts to prevent splashing of mercury to the top of the housing and to provide a fillet of mercury at the intersection between the top plate and the armature which appears to damp the mechanical rebound of the armature on engaging the contact surfaces. Further, the armature is made narrower than the adjacent terminals to prevent excessive mercury from collecting on the adjacent side walls of the housing and flooding the contacts.

Many other objects and advantages of the present invention will become apparent from considering the following detailed description in conjunction with the drawings in which:

FIG. 1 is a sectional view of a mercury-wetted contact unit embodying the present invention;

FIG. 2 is an enlarged sectional view taken along line 2-2 in FIG. 1; and

FIG. 3 is a sectional view taken along line 3--3 in FIG. 2.

Referring now more specifically to FIG. 1 of the drawings, therein is illustrated a mercury-wetted contact unit or switch which is indicated generally as and which embodies the present invention. The contact unit 10 includes an elongated insulating or glass housing or tube 12 in the upper end of which a pair of magnetic and electrically conductive terminals 14 and 16 are sealed with their lower or inner end portions 14A and 16A disposed within a sealed cavity 18 formed by the housing 12. A hollow header 20 forming a part of an armature support assembly is sealed in the other or lower end of the housing 12 and carries at its upper end a hinge or pivotal support assembly indicated generally as 22 which pivotally or hingedly mounts the lower end of a short, rigid, and mercury-wetted armature structure 24.

The upper end of the armature structure 24 is interposed between the terminal portions 14A and 16A and is adapted to alternately engage these terminals to establish conductive electric circuits from the header 20 to alternate ones of these terminals, the terminals 14 and 16 providing motion limiting means for limiting pivotal movement of the armature 24 under the influence of an applied magnetic field. The pivotal mounting for the short rigid armature 24 afiorded by the assembly 22 is such that the armature structure 24 is completely free of mechanical bias or stress and is free to move to the positions determined by engagement with the terminal portions 14A and 16A. This free pivotal movement for the short rigid armature 24 permits the switch 10 to provide substantially jitter free operations at operating speeds or rates up to eight hundred cycles per second.

The hollow header 20 which forms a support for the pivotal mounting assembly 22 includes an opening 26 through which the mercury forming a reservoir pool 28 is introduced into the cavity 18 of the sealed contact unit 10 using an axially extending passage 30 in the header 20. The opening 26 and the passage 30 are also used to control the establishment of the desired atmosphere, such as hydrogen, within the cavity 18. The passage 30 is then sealed by swaging the outer end of the header 20 to form a flattened portion 20A to which a crosspiece 32 is welded. The header 20 is preferably formed of magnetic material. The inner end is also swaged or otherwise formed to form a flat portion 20B for supporting the pivotal support assembly 22. The portions of the header 20 disposed within the cavity 18 can be wetted with mercury to provide an elongated path over which mercury from the pool 28 can move to the assembly 22.

The assembly 22 for hingedly or pivotally mounting the armature 24 includes a generally U-shaped member 34 having a bight portion 34A welded or otherwise secured to the upper end of the fiat portion 20B and a pair of spaced arms 34B and 34C. The two arms 34B and 340 are provided with aligned openings such as an opening 36 in the arm 34C (FIG. 2) in which is pivotally or rotatably received a pivot pin 38. The lower end of the armature 24 is provided with an arcuate section 24A (FIG. 3) that is secured, as by spot welding at the point 39 indicated in dashed outline in FIG. 2, to the pivot pin 38.

In a sealed mercury contact unit 10 constructed in accordance with the present invention, a maximum clearance of .0007 inch is provided between the pivot pin 38 and the contiguous walls defining the openings 36, and a maximum clearance of .0004 inch is provided between the edges of the armature 24 and the adjacent walls of the arms 34B and 34C so that these arms maintain the armature 24 in its predetermined position. The materials forming the elements 34 and 38 are wetted with mercury for the purpose of providing a path over which mercury can flow from the pool 28 to the armature 24 and for the purpose of lubricating the pivotal movement between the parts 34 and 38. With these clearances and with mercury-wetted material forming the parts 24, 34, and 38, all relative movement of the parts is lubricated by the mercury, and no appreciable change in the indicated clearances is noted even after operating a switch through six billion operations. Thus, the pivotal supporting assembly 22 mounts the armature 24 for pivotal or hinged movement completely free of any restraining forces or stresses.

The armature 24 is formed of magnetic material and is of a generally uniplanar, somewhat elongated rectangular configuration having grooves formed on its two planar surfaces to provide capillary surfaces for transmitting mercury from the pivotal supporting assembly 22 to the contact surfaces of the armature which are disposed adjacent its upper end between the portions 14A and 16A of the terminals 14 and 16. Thus, the pivotal supporting assembly 22 provides, in effect, a limited reservoir of mercury spaced from the pool 28. This pool is adequate to supply a sufficient quantity of mercury to wet the grooved planar surfaces of the armature 24 with mercury, while the elongated path of mercury-wetted surfaces between the assembly 22 and the pool 28 prevents such a flow of mercury as would permit the accumulation of excessive amounts of mercury at the top of the armature 24 when the sealed contact unit 10 is operated at the high speeds for which it is designed.

The sealed contact unit 10 provides break-before-make contact action so that, for instance, the continuity of the electrical circuit between the armature and the terminal 16 is interrupted before an electrical circuit is established between this armature and the terminal 14. To accomplish this, the portions 14A and 16A of the terminals 14 and 16 are provided with contact elements 40 and 42, respectively, having planar surfaces that are wetted with mercury and engaged by opposite surfaces of the upper end of the armature 24. The remaining surfaces of the contacts 40 and 42 as well as the contiguous portions 14A and 16A of the terminals 14 and 16 are treated, as by plating with chromium, so as to be incapable of wetting with mercury. The terminals and contacts can be formed, for instance, as described in detail in United States Patent No. 3,331,037. The engaged planar surfaces of the contacts 40 and 42 and of the armature 24 are supplied with enough mercury to provide mercury-wetted contact action, but with insufficient mercury to bridge the contacts 40 and 42. Thus, the switch or sealed contact unit 10 provides non-bridging or make-before-break contact action. By wetting the entirety of the contacts 40, 42 or by reducing the gap between these contacts, the switch 10 can provide bridging contact action.

In prior or conventional mercury-wetted contact switches, the armature is center stable or mechanically centered between the two fixed contacts so that when the armature is actuated between the contacts, a mechanical biasing or restraining force begins to retard the motion of the armature as it passes through the center position. This restraining force in prior switches tends to prevent severe coining of the armature and the fixed contacts. In the switch 10, because of the freely pivoted or hinged armature, there are no forces acting to tend to decelerate the armature as it moves from one contact to the other contact, and severe coining of the fixed contacts can occur. Accordingly, it is necessary to reduce the mass of the armature structure 24 and the arc through which the armature 24 is moved to the greatest extent possible so as to avoid coining or swaging of the fixed contacts 40 and 42. Accordingly, the upper end of the armature 24 terminates immediately above the fixed contacts 40 and 42, and in a typical sealed switch unit 10 constructed in accordance with the present invention, the anmature has a length of between .100 and .200 inch, e.g., .133 inch, a thickness of .005 to .007 inch, and a width of between .03 and .04 inch, e.g., .036 inch. Considered relative to the axis of pivotal movement of the pin 38, the armature 24 is pivoted through an arc of between 3 and 4", with the gap between opposed planar surfaces of the contacts 40 and 42 being set at around .013.0l5 inch.

In order to limit the splashing of mercury toward the upper end of the unit 10, two opposed troughs or recessed areas 44 and 46 are formed in the portions 14A and 16A of the terminals 14 and 16, and a plate 48 is secured to the upper end of the armature 24 extending substantially perpendicular thereto. The length of the plate as viewed in FIG. 3 is equal to approximately twice the separation between the contacts 40 and 42 and cooperates with the recessed areas 44 and 46 to prevent splashing of mercury above the contacts 40 and 42. The plate 48, which is formed of magnetic material to improve the sensitivtiy of the unit 10, is also wetted with mercury and tends to form fillets of mercury at the intersections of the armature 24 and the plate 48. These fillets of mercury provide a reservoir of :mercury for wetting the engaged surfaces of the contacts 40 and 42 and the armature 24, and also provides means for limiting mechanical rebound of the armature 24 as it engages either of the contacts 40 and 42. More specifically, it appears that the mass of the fillet of mercury tends to distort in configuration, but does not separate from the armature 24 and the top plate 48 as the armature strikes the contacts 40 and 42. This distortion appears to absorb part of the energy of impact between the armature 24 and the contacts 40 and 42 so that the mechanical rebound of the freely pivoted armature 24 is actually less than the mechanical rebound encountered in conventional switches, which as set forth above, are subject to a restraining force due to mechanical stressing of the flexible armatures used in prior mercury switch constructions.

Further, some of the very elastic droplets of mercury liberated when the armature 24 strikes the contacts 40 and 42 move away from the contacts 40, 42 in a direction away from the armature 24 and at an angle to the terminal portions 14A and 16A. If the armature 24 is wider than the terminal portions 14A and 16A or is not centered (FIG. 2) with respect thereto, these mercury droplets accumulate on the side walls of the housing 12 and may flood the contacts 40 and 42 or cause inadvertent bridging thereof. To avoid this, it has been determined that if the armature 24 is made narrower than the terminal portions 14A, 16A (FIG. 2), the droplets tend to strike these terminal portions and ultimately return to the capillary system of the switch without excessive accumulation on the adjacent walls of the glass envelope 12.

In one application of the sealed contact unit or switch 10 in a relay, opposite magnetic biases are applied to the terminals 14 and 16 by one or a plurality of magnets, and the switch 10 is then placed within an operating coil provided, for instance, with a sinusoidal input signal. The oppositely poled biases applied to the terminals 14 and '16 coupled with the oppositely directed undulations in the input signal applied to the operating coil transfer the short rigid armature 24 into alternate engagement with the contacts 40 and 42. In one such relay supplied with a six hundred c.p.s. sine wave input signal, more than six billion operations have been obtained without substantial variation in the operating characteristics of the switch. The switch is capable of switching a one hundred watt load without contact welding or deterioration with an operate time of less than .5 millisecond. The switch is also quite desirable for low signal level switching because the lack of mechanical rebound reduces contact noise to an extremely low level. Any jitter encountered has a persistence of less than fifty microseconds.

Although the present invention has been described with reference to a single illustrative embodiment thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this invention.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. A mercury-wetted contact unit comprising an elongated insulating housing forming a sealed cavity,

a pair of motion limiting members carried on the housing and disposed at spaced positions within the cavity, at least one of the motion limiting members providing an electrical conductor having a contact surface,

an armature support assembly sealed in one end of the housing and extending into the cavity,

an elongated rigid armature structure having a free end portion movable into engagement with alternate ones of the motion limiting members and engaging said contact surface on said one motion limiting wetted and having a length in the direction of its elongation measured from its free end to its pivotal mounting axis that is in the range from .100 to .200 inch,

a pivotal mounting structure interconnecting the other end of the armature structure and the armature support assembly and affording unbiased movement of the rigid armature structure over an arcuate path of 3-4 limited by engagement of the free end of the armature structure with the spaced motion limiting members,

and a pool of mercury in the housing at the end thereof in which is sealed the armature support assembly, the armature support assembly having a mercurywetted surface to provide a path for movement of the mercury from the pool to the armature.

2. A mercury switch unit comprising a sealed insulating housing,

a pair of spaced contacts sealed in one end of the housan armature support assembly sealed in another end of the housing,

a rigid armature structure having a capillary surface, one end of the armature structure being disposed between the spaced contacts,

said armature support assembly and the other end of the armature structure including pivot pin means and a bearing structure receiving the pivot pin means that mount said other end of the rigid armature structure on the armature support assembly for pivotal movement free of mechanical stress and limited only by the engagement of said one end of the armature structure with the spaced contacts,

and a mass of mercury disposed within the housing adjacent the seal between the housing and the armature support assembly for wetting the capillary surface of the armature structure,

the portion of said armature support assembly disposed within the housing having a mercury wetted surface for conveying mercury from the mass to the lower end of the armature structure for subsequent movement along the capillary surface to a point adjacent the spaced contacts, the length of path along the sur faces of the armature support assembly being long with respect to the length of the path along the capillary surface to limit the amount of mercury that can move into proximity to the spaced contacts.

3. The mercury switch unit set forth in claim 2 in which the pivot pin means and the bearing structure are mercury-wetted to lubricate-pivotal movement of the armature structure.

4. The mercury switch unit set forth in claim 2 in which the spaced contacts are formed with recessed areas located opposite each other,

and the armature structure includes a transversely extending member carried on its free end movable into the recessed areas on alternate ones of the spaced contacts. 5. The mercury switch unit set forth in claim which the spaced contacts each include a mercury-wetted surface engaged by the armature structure, the remaining surfaces of the spaced contacts adjacent the armature structure being incapable of being wetted with mercury. 6. The mercury switch unit set forth in claim 2 in which the pivot pin means is rigidly secured to the armature structure, and the bearing structure is carried on the armature support assembly and includes a pair of spaced and apertured arms pivotally receiving the ends of the pivot pin means with the armature disposed between the arms. 7. The mercury switch unit set forth in claim 6 in which the bearing structure and the pivot pin are wetted with mercury. 8. The mercury switch unit set forth in claim 6 in which the armature support assembly includes a hollow sleevelike member sealed in the housing and having a generally uniplanar end portion to which the bearing structure is secured. 9. A mercury-wetted contact unit comprising an elongated insulating housing forming a sealed cavity,

a pair of motion limiting members carried on one end of the housing and disposed at spaced positions within the cavity, at least one of the motion limiting members providing an electrical conductor having a contact surface,

a mercury-wetted armature support assembly carried on the other end of the housing within the cavity,

a pool of mercury within the cavity at said other end of the housing, 1 p w an elongated rigid armature structure having a free end portion movable into engagement with alternate ones of the motion limiting members and engaging said contact surface on said one motion limiting member, said armature structure being mercurywetted,

and a pivotal mounting structure interconnecting the other end of the armature structure and the armature support assembly and atfording unbiased movement of the rigid armature structure, said pivotal mounting structure being spaced substantially above the mercury pool by the armature support assembly so that mercury from the pool can reach the armature structure only after movement along an elongated path on the mercury-wetted surfaces of the armature support assembly.

10. A mercury switch unit comprising a sealed insulating housing,

a pair of spaced terminals sealed in one end of the housing and each having a contact and a recessed area disposed above the contact, said contacts being spaced a given distance,

an armature support assembly sealed in another end of the housing,

a rigid and generally uniplanar armature structure having a capillary surface, one end of the armature structure being disposed between the spaced contacts and terminating adjacent the recessed areas in the terminals,

said armature support assembly and the other end of the armature structure including structure mounting said other end of the rigid armature structure on the armature support assembly for free pivotal movement limited by the engagement of said one end of the armature structure with the spaced contacts,

a mass of mercury disposed within the housing for wetting the capillary surface of the armature structure,

and a member secured to said one end of the armature structure extending substantially perpendicular thereto, said member having a length at least as great as said given distance and extending into said recessed area as the armature structure is pivoted.

References Cited UNITED STATES PATENTS 2,037,535 4/1936 Rankin 335154 3,051,805 8/1962 Binford 325-205 3,054,873 9/1962 OBrien 335-58 3,331,037 7/1967 Hempel 33558 5 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner 

